Fix ctgenstructure_unittest

As I mention in the commit message, I'm not sure if these tests are all that helpful, and could suitably be replaced with internal function unit tests for the `parse_cueparams` routine in parser.c. That can be done in a later patch though.

Commit messages:
```
load correct filenames in ctgenstructure_unittest

I'm not sure if these tests are specifically needed anymore, I think
these ones should be replaced with internal unittests for the
parse_cueparams routine, that way we can avoid all the test renaming
kerfuffel and have more meaningful test results.

removed ctgenstructure_unittest from XFAIL_TESTS
```